Mobile robot with manipulator systems are widely used in various fields for its mobility and portability. However, its position accuracy is not sufficiently high for delicate applications. Conversely, a robot arm has higher position accuracy and fast reaction speed but limited reachability or workspace.
An area of interest is that of surface tracking by a mobile robot/manipulator. For example, a mobile manipulator may need to follow a surface at a distance therebetween. Example applications include large structure inspection (e.g., welding and welding seam inspection), store checking (e.g., book scanning in a library) and painting in shipyards. These types of applications require the robot to maintain a close distance from the surface. Furthermore, servicing applications (e.g. table and window cleaning) and industrial applications (e.g., cutting and polishing) require contact between the surface and the end-effector of the mobile manipulator. Therefore, large tracking error would either result in losing contact with or excessive contact force being exerted on the surface.
There exist conventional methods such as Simultaneous Localization and Mapping (SLAM) for navigation. However, such conventional methods do not achieve a sufficient degree of accuracy in surface tracking in order to be suitable for various applications such as the applications as mentioned above. In such conventional methods, typically, the robot location is determined by comparing the sensor reading with the map, which has limited resolution. An accurate map with high resolution will result in large map files and slow down computation. This implies that with such conventional methods, the relative position between the mobile manipulator and the surface cannot be determined to an accuracy that is sufficient for various applications.
A need therefore exists to provide a method of controlling a mobile manipulator for tracking/following a surface with sufficient accuracy for various applications. It is against this background that the present invention has been developed.